This invention relates to a cylindrical cutter head for cutting holes in metal objects and particularly irregular metal objects so that the holes have improved cylindricality. An example of the application of the cutter head is for cutting a hole in a pipe wall. It can be easily understood that when cutting a relatively large diameter hole in the wall of a relatively large diameter pipe that the tubular cutter head undergoes substantial stress during the cutting action. The reason is that when cutting initially starts the tubular cutter head engages the pipe only on portions that are 180.degree. apart. As the cutting depth increases the amount of contact of the cutter head with the pipe wall increases but usually the full 360.degree. of the cutting head does not contact the pipe at the same time. Since the sidewall of a tubular cutter head is preferably relatively thin the forces encountered during cutting operations can cause the sidewall to deflect, thus, either forming an irregular shaped hole or causing more rapid wear on the teeth of the cutter head.
A cutter head having a tubular sidewall should ideally remain symmetrically circular throughout the cutting operation so that cutting action does not vary with respect to the axis of rotation of the boring bar or other member by which the cutter head is rotated.
It is normally desirable that the tubular sidewall of a cutter head be relatively thin. This is so since the tubular sidewall must be no greater in thickness than the width of the cutting teeth. Obviously, the wider the cutting teeth the more metal is removed to cut a hole and more force that is required to form a hole in a pipe or other object. Ideally, the width of the teeth of a tubular boring portion of a cutter head is as narrow as possible to reduce the cutting energy required. The sidewall must follow the teeth through the hole as it is cut. This means that ideally a cutter head tubular sidewall needs to be as thin as possible but, at the same time, it must have sufficient rigidity to withstand the forces that are encountered in cutting through an irregular object while preserving its concentricity about its rotational axis.
Others have provided cutting heads for cutting large diameter holes in metal objects such as illustrated in U.S. Pat. Nos. 1,441,994 issued to Mueller entitled "Shell Cutter And Drill For Drilling Machines"; 1,855,873 issued to Shortell entitled "Cutting Tool"; 4,422,812 issued to Linville entitled "Rotatable Shell Cutter"; 4,616,965 issued to Anderson et al entitled "Indexable Shell Cutter" and 4,968,192 issued to Hamilton entitled "Trepanning Tool". Each of these patents show a cutter head having a cutting member with a relatively thin tubular wall and a head portion that attaches to the tubular cutting member. In most of these prior issued patents the rotatable head is of a relatively thick material that is substantially greater in thickness than that of the annular cutting member. None of these patents show devices where the head portion is configured to deflect or otherwise change the force applied to the annular cutting member tubular sidewall in the process of cutting a large diameter hole.
Since, as previously stated, a shell cutter typically has a relatively thin wall that is used to cut a hole through an uneven object, such as the wall of a pipe, the cutter shell is sometimes slightly deflected causing the hole formed by the cutter to depart from cylindricality. In many applications, it is highly desirable that the hole formed, such as the wall of a metal pipe, be as cylindrical as is practically possible. An object of this invention is to provide an improved shell cutter having means to hone or polish a hole cut in a pipe so as to improve the cylindricality of the hole.
Another object of the present invention is to provide an improved cutter shell having a boring portion with a tubular sidewall with teeth at the forward circumferential end and having an increased diameter abrasive band spaced above the teeth and having an inverted dish shaped head portion of relatively thin material. The head portion deflects in response to boring pressure. The deflection serves to apply force to the circumferential upper end of the tubular boring portion to stiffen and make it more resistant to deflection to thereby reduce the possibility of the boring portion tubular sidewall taking a non-circular shape during a boring operation.
After the teeth have passed through the object being cut, such as a wall of a pipe, the hole formed in the object is engaged by the abrasive band. The abrasive band serves to hone the internal circumferential surface of the hole to remove irregularities and to provide a finished hole that is more nearly perfectly cylindrical than is normally attained with a shell cutter, particularly, a shell cutter of the type having a relatively thin wall.